Television camera comprising a diaphragm control and a controllable picture signal amplification circuit

Abstract

A television camera having a diaphragm control and a controlled picture signal amplification circuit for keeping a picture signal value substantially constant. A single control system is formed by having the diaphragm opening adjusting element perform the gain control through an electronic control circuit, which takes place at low scene light intensities only. In the automatic control the amplified picture signal is utilized directly for the diaphragm control and, at low light intensities, indirectly for the gain control. With manual control the operator directly influences the diaphragm adjusting element and, consequently, indirectly the gain control at low light intensities. In the automatic control no discontinuities occur in the control characteristic and with manual control operation is simplified.

What is claimed is: 
     
       1. A television camera comprising a diaphragm control and a gain controllable picture signal amplification circuit for keeping a picture signal value substantially constant at varying scene light intensities, an adjusting element for adjusting the diaphragm opening, the diaphragm control being mainly operative at a scene having higher light intensities and the control of the picture signal amplification circuit mainly taking place at lower scene light intensities, an electronic control circuit coupled to the adjusting element, said control circuit having a first signal output coupled to a control signal input of the picture signal amplification circuit for providing that at lower scene light intensities and upon a readjustment of the adjusting element and a consequent change of the diaphragm opening simultaneously a change of the gain factor of the picture signal gain circuit occurs. 
     
     
       2. A television camera as claimed in claim 1, wherein the camera comprises a switching circuit for switching the diaphragm control off or on respectively, the adjusting element for the diaphragm opening having an element for manual operation. 
     
     
       3. a television camera as claimed in claim 1, wherein the camera comprises a signal comparison circuit, and a switching over circuit having at least a first and a second selector contact and a master contact, the master contact being coupled to the diaphragm adjusting element for the control thereof, the first selector contact associated with an automatic control being coupled through said signal comparison circuit to the output of the picture signal amplification circuit, and the second selector contact associated with a manual operation being connected to an adjustable bias voltage. 
     
     
       4. A television camera as claimed in claim 1 wherein the picture signal amplification circuit has a non-linearly controlled gain factor. 
     
     
       5. A television camera as claimed in claim 4, wherein the controlled gain factor has a substantially hyperbolical variation. 
     
     
       6. A television camera as claimed in claim 1, further comprises a lowpass filter series coupled to said picture signal amplification circuit, and wherein said electronic control circuit has a second signal output which is coupled to a switch-on and switch off control signal input of said lowpass filter. 
     
     
       7. A television camera as claimed in claim 6, wherein the electronic control circuit comprises a first and a second threshold circuit coupled to the first and the second signal outputs respectively, the signal threshold of the second threshold circuit being passible after that of the first threshold circuit for supplying an output signal. 
     
     
       8. A television camera as claimed in claim 6 wherein the lowpass filter has a frequency pass band from 0 to the order of magnitude of approximately 3 MHz. 
     
     
       9. A television camera as claimed in claim 1, suitable for colour television, wherein the camera comprises several picture signal channels, each signal channel comprising one of said picture signal amplification circuit, the control signal inputs being interconnected and coupled to the first signal output of the control circuit.